Damping magnet assembly



Oct. 12, 1954 G. e. WAITE ETAL 2,691,763

DAMPING MAGNET ASSEMBLY Filed Feb. 2, 1951 5 mmvroxs. Griffin/G. ZZ/cZzZ e, BY [uarfffg Patented Oct. 12, 1954 UNITED STATES PATENT OFFICE DAMPING MAGNET ASSEMBLY Griflin G. Waite, Toronto, Ontario, and Ivar K.

- F08, King Township, Ontario, Canada, assignors to Sangamo Electric Company, Springfield, 111., a corporation of Illinois Application February 2,1951, Serial No. 209,028

9 Claims. 1

This invention relates to damping magnet assembly for induction meters such as watthour meters and the like.

In induction disc meters a disc of conductive material is driven by the meter coils and its rotation is a measure of the electrical energy in the metered circuit. Such meters normally employ .a permanent damping magnet and associated armature arranged on opposite sides of the disc so that magnetic flux through the armature cuts the disc, producing currents in the disc which act to retard disc rotation.

The damping magnet forms a convenient means of calibrating the meter and it has been proposed to provide a variable shunt for the magnetic flux to control the flow of flux through the disc for calibration.

It has also been proposed to vary the separation or air gap between the elements of the magnet assembly as a calibration control.

The principal object of this invention is to provide a novel damping magnet assembly having an improved calibration control giving continuous adjustment of retarding torque over a wide range.

A further object is to provide a magnet assembly which will be simple to adjust and will hold adjustment against accidental movement under normal handling of the meter.

Another object is to provide a compact and rugged magnet assembly of relatively inexpensive construction.

A further object is to provide for protection 'of the magnet from demagnetization from adjacent fields.

A still further object is to provide for effective temperature compensation without upsetting calibration adjustment.

The principal feature of the invention consists in varying the reluctance path afforded the flux traversing the disc without altering the separation between the planes of the armature and disc.

According to the invention the reluctance of the flux path is varied by providing the armature with a magnetic restriction, and mounting the magnet and armature for relative movement without altering their separation, in a manner whereby the magnetic restriction may be moved between one position in the path of magnetic flux through the armature between the magnet poles, and another position substantially clear of the flux path, providing a continuous variation of reluctance through the armature from maximum to minimum. p

The magnetic restriction may conveniently be provided by reducing the cross section of the armature, and in one particular concept of the invention as depicted herein the armature is formed as a rotatable disc having slots in the face thereof movable upon armature rotation into and out of registration with the magnet pole faces.

A further feature of the invention consists in employing a friction member to hold the armature in adjusted position.

Still a further feature consists in providing a temperature compensating shunt bridging the magnetic poles and operating independently of the calibrating variable reluctance armature.

' These and other objects and features will become apparent from the following description of the specific form of the invention taken in conjunction with-the accompanying drawings, in which,

Figure -l is'an elevational view of the permanent magnet assembly and armature mounts Figure 2 is a view similar to Figure l but showing the armature in position and the induction disc received between the armature and magnet pole faces.

Figure 3 is an underside plan view of the device of Figures 1 and. 2.

Figure 4 is a top side plan view of the devices of Figures 1 and 2.

Figure 5 is a top plan view of the permanent magnet and mounting with the armature removed and armature mounting partly in section.

Figure 6 is a diagrammatic illustration showing the relation of the armature and pole faces for maximum reluctance.

Figure '7 is a view similar to Figure 6 but showing the armature turned to an intermediate position.

Figure 8 is an underside plan of the armature with the armature mount in section and showing the magnet pole faces in dotted lines to illustrate the relative position of the armature and a mount for the armature mount 1 secured thereto by rivets 8. The armature mount or bracket I is of yoke form and is provided with broad lateral wings 9 affording at the same time the' means for connecting the armature mount to the permanent magnet casting and a magnetic shield for the permanent magnet assembly shielding the assembly against the magnetizing effects of adjacent fields such as encountered in a watthour meter.

The armature 2 is rotatably supported from the armature mount above the pole faces 4 by a bolt l passing through the armature mount and threading into the armature.

A Phosphor bronze spring in the form of a toothed disc H is located under the head: of the l bolt l0 and acts to maintain the bolt and armature 2 against accidental rotation.

The armature is formed of aplurality of laminations l2 of magnetic material, and the outer of these laminations are provided with diametrically disposed slots 13. The slots are parallel, and in one position of the armature, as illustrated diagrammatically in Figure 6, overlie or register with the pole faces 4 of the permanent magnet assembly, being in area an appreciable portion of the area of the pole faces. The axis of rotation of the armature coinciding with the axis of the bolt I0 is at the centre of the armature, here depicted as of circular form and coincides with the threaded bore l4 into which the tip of' the bolt, which operates freely through the armature mount, is threaded.

Figure 7 illustrates the armature turned through 45 so that only a portion of the slots or recesses l3 are in registration with the pole faces.

It will be understood that in the magnetic path between the pole faces in Figure 6 there is appreciably less metal affording a flux path with the slots directly over the pole faces than with the slots turned to the position of Figure '7, and the effective air gap between the pole faces and armature is increased without any relative movement therebetween in the direction of the air gap.

In Figure 8 the armature is illustrated as turned through afurther 45 from Figure 7. The size and spacing of the recesses in this position places them substantially outside the armature path between the pole faces. Therefore the amount of armature metal affording a flux path is further increased and the effective air gap is decreased. The result is a material decrease in the reluctance offered to the armature flux.

As the armature can be rotated smoothly between the positions of Figures 6 and 8 a continuous variation in the reluctance of the flux path from the maximum of Figure 6 to the minimum of Figure 8 can be obtained as the cross section of metal available to carry the flux continuously increases from a minimum to a maximum and the effective air gap reluctance continuously decreases from a maximum to minimum.

The actual manner in which the reluctance varies depends upon the shape of the recesses 13 in the armature relative to the shape of the pole faces 4, to give control over the character of the meter calibration.

The additional factors afiecting character of the calibration and additionally controlling the total range of calibration are the thickness of the laminations l2 and their number employed, provided that sufficient metal is afforded to carry the total flux to be conveyed. through the armature. By control of these factors, recess shape, armature configuration, and lamination thickness and number, that is, metal available as a flux path, a linear or non-linear calibration curve can be obtained by control of these factors.

In the particular embodiment of the invention illustrated herein substantially linear calibration is obtained.

For convenience in operating the armature a plurality of slots l5 are provided in its periphery of a size to receive the blade of a screwdriver or the like;

The adjustment of the armature carried out by moving the armature in its own plane provides for variation of the flux through the armature, and hence. provides for variation of the flux cutting the induction disc l6 of the watthour meter or the like, so as to control the damping afforded by the assembly on the disc I6 in order to provide the calibration referred to above without bodily altering the separation of the magnet and armature.

Thus the inaccuracies and rough control afforded by bodily moving the armature towards or away from the magnet is eliminated as is also the disadvantage of moving the whole magnet assembly. In addition the reluctance path through the disc [6 is controllable Without requiring any complicated shunt arrangement.

The arrangement of having the recesses 13 move over the pole faces and increase the effective air gap permits a very marked variation in the armature reluctance to be obtained upon armature movement.

As illustrated in Figure 2, the pole faces 4 are undercut at IT to provide a groove for the reception of a temperature compensating shunt 18 having a negative temperature co-efficient of permeability, the shunting effect of which decreases with increasing temperature to compensate for tendency of the disc 13 to speed up under increasing temperatures as is well understood in the art.

It will be noted that with the present invention the temperature compensating shunt l8 does not alter the reluctance of the armature path and hence does not effect the calibration setting, as for instance may occur when calibration is made to depend upon an adjustable shunt in parallel with the temperature compensating shunt.

The particular construction depicted herein utilizing air in the recesses Hi to afford the magnetic restriction is desirable in that it provides in an extremely compact form an armature made solely from high permeability armature metal which is continuously adjustable in reluctance value between the magnet pole faces, from minimum to maximum.

However it will be appreciated that the invention is not limited to the specific armature depicted herein nor to armatures mounted. solely for rotation, and the invention may be carried out by mounting the armature for movement in its own plane other than rotation to alter the cross section of the armature metal path and hence the reluctance afforded the magnetic flux traversing between the magnet pole faces.

What we claim as our invention is:

l. A damping magnet assembly for an induction disc type meter comprising a permanent magnet assembly having a pair of spaced pole faces and a magnetic armature spaced opposite said pole faces and parallel thereto to define an induction disc receiving slot therebetween, said magnet and armature being mounted so as to be capable of relative rotary movement in. a direction parallel to said pole faces without altering the gap spacing between said magnet and armature, said armature having two restrictions in cross section taken perpendicularly to the plane thereof, and located to be introduced into the path of armature flux between said pole faces upon such relative rotary movement of said armature and magnet to vary the magnetic reluctance offered to said armature flux. said two restrictions being of like general shape and being symmetrically disposed with respect to the axis of rotation of said armature for acting with like effect upon the two gaps at said two pole faces in the rotative adjustment of said armature- 2. A damping magnet assembly for an induction disc type meter comprising a permanent magnet assembly having a pair of spaced pole faces, a rotatable magnetic armature formed to constitute throughout different areas different paths differing in magnetic reluctance, and means mounting said armature in a position bridging and spaced from said pole faces so as to be capable of rotati-ze movement parallel thereto without altering the gap spacing between said magnet and armature whereby to alter the portion of said armature in bridge across said pole faces and hence vary the magnetic reluctance offered armature flux between said pole faces, said different reluctance paths in said armature being arranged to act substantially equally on the fluxes at both pole faces in each position 01' rotative adjustment of said armature.

3. A damping magnet assembly for an induction disc type meter comprising a permanent magnet assembly having a pair of spaced coplanar pole faces, a magnetic armature mounted in spaced relation to' and parallel with said pole faces to define a disc-receiving slot therewith,

said armature being formed with two spaced cross sectional restrictions each adapted to coact with one of said permanent magnet pole faces for affording an increase in magnetic reluctance in any path through said armature including said restrictions, each restriction being of lesser area than the area of its associated pole face, and means enabling movement of said armature around an axis of rotation and in a plane parallel with said pole faces to introduce said cross sectional restrictions progressively into the path of flux traversing said armature between said pole faces.

4. A damping magnet assembly, comprising a permanent horseshoe magnet embedded in a nonmagnetic casting and presenting a pair of spaced exposed pole faces, an armature mount carried by said casting, an armature composed of magnetic material supported on said armature mount for movement in a plane parallel to said pole faces and defining with said pole faces an induction disc-receiving slot, said armature having magnetic restriction means positioned to be shifted by movement of said armature between a position where said magnetic restriction means is included in the path of flux which traverses said armature between said pole faces and a position where it is substantially clear of said flux path,

6 said magnetic restriction means acting to substantially the same degree on the fluxes at both of said pole faces in the different positions of adjustment of said armature.

5. A device as claimed in claim 4 in which said armature is rotatable and said magnetic restriction means comprises a restriction in the cross section of said armature displaced from the centre of rotation.

6. A damping magnet assembly, comprising a permanent magnet assembly embedded in a nonmagnetic casting and presenting a pair of spaced exposed pole faces of relatively long narrow form, an armature mount extending over said pole faces, a magnetic armature disc rotatably supported on said mount above said pole faces and defining therewith a slot to receive an induction disc, said armature disc having a pair of diametrically disposed recesses in the surface thereof also of relatively long narrow form located to move between a position aligning with said pole faces and a position substantially clear of said pole faces and outwardly thereof upon rotation of said disc.

7. A damping magnet assembly, comprising a permanent magnet assembly embedded in a nonmagnetic casting and presenting a pair of spaced exposed pole faces, an armature mount in the form of a yoke secured to said casting and bridging said pole faces, an armature composed of magnetic material in the form of a disc supported from said mount in spaced relation to and bridging said pole faces to rotate about an axis located centrally between said pole faces and perpendicular thereto, said disc having a pair of diametrically disposed recesses extending into the surface thereof and spaced from the axis of rotation substantially one-half the separation of said pole faces and moving between a position aligning with said pole faces and a position at right angles thereto and substantially outwardly of said pole faces, spring means holding said disc in adjusted positions of rotation, and a temperature compensating shunt element arranged between said pole faces.

8. A device as claimed in claim 7, in which the periphery of said disc is slotted to receive a tool for turning said disc.

9. A device as claimed in claim 7, in which said disc is supported by a bolt passing through said armature yoke and threaded into said disc, and said spring means comprises a spring washer introduced under the head of said bolt and engaging said yoke.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,686,727 Bradshaw Oct. 9, 1928 1,772,091 Stein Aug, 5, 1930 2,149,288 Green Mar. 7, 1939 ,284,893 Barnes June 2, 1942 

